Glass is generally composed of inorganic oxides, and contains silicon dioxide (SiO.sub.2), also known as silica, as the major constituent. Suitable feed materials for glassmaking include silica as the major component with feldspar as a minor component. Feldspar provides alumina which acts as a flux during glassmaking.
A flotation process is commonly used to produce a feldspar-containing concentrate from naturally-occurring deposits. The concentrate is shipped to the plant and blended with locally available silica to form the feed material. The flotation process generally includes the steps of crushing and grinding the material to a relatively small size, conditioning with a promoter, such as hydrofluoric acid, sulfuric acid, sodium fluoride, or hydrochloric acid, to provide a pH of pH 2 to pH 3 and floating the ground material in the presence of the promoter to form the feldspar-containing concentrate which is required to contain minimum amounts of mica, heavy minerals and iron-containing compounds, and a waste product (commonly referred to as "tailings"). As used herein, "iron impurities" are any inorganic or organic compounds that contain iron and are ferromagnetic or paramagnetic. Iron is detrimental to glassmaking because iron can discolor the glass. Heavy mineral impurities are any metal-containing compounds that have a melting point of more than about 2900.degree. F. Heavy mineral impurities, particularly refractory heavy minerals (e.g., silliminite and kaynite) are not melted during the glass melting process and can become embedded in the finished glass as a solid inclusion or a "stone" defect. Exemplary heavy minerals include the sillimanite minerals (e.g., corundum, zircon, topaz, spinel, chromite, andalusite, cassiterite, and chrysoberyl).
The flotation techniques used to form the feldspar concentrate use expensive and environmentally hazardous reagents, such as hydrofluoric acid, sulfuric acid, or sodium fluoride. The use of these chemicals can add significantly to the cost of processing the raw material and can create problems in disposing of the water used in flotation. Some chemicals require a special tailings disposal method, thus adding to the overall cost of the glassmaking process.
Therefore, there is a need for an inexpensive method for forming a feed material for glassmaking.
There is a further need for a method for forming a feed material for glassmaking that does not require the use of hazardous chemicals.